The present invention concerns a method of recovering hydrocarbons from underground formations by the use of a microemulsion comprising lignin and amine components.
A microemulsion is a stable, clear or translucent solution comprised of oil, water, and surfactant. The microemulsion may also contain one or more electrolytes, cosurfactants, and when used for enhanced oil recovery, water-soluble polymers and sacrificial agents. The droplet diameters of the dispersed phase range from roughly 140 to 10 nanometers.
Microemulsions may be classified as oil-in-water microemulsions, water-in-oil microemulsions, and middle-phase microemulsions. An oil-in-water microemulsion is a microemulsion in which the external or continuous phase is water and the dispersed phase is oil. A surfactant-water mixture which forms an oil-in-water microemulsion can equilibrate as a single phase or as two phases such as a lower phase oil-in-water microemulsion plus an equilibrium upper phase of oil, depending on the overall composition of the mixture. Such mixtures are defined by those skilled in the art of surfactant flooding as existing in a Type II(-) phase environment.
A water-in-oil microemulsion is a microemulsion in which the external or continuous phase is oil and the dispersed phase is water. A surfactant-oil-water mixture which forms a water-in-oil microemulsion can equilibrate as a single phase or as two phases such as an upper phase water-in-oil microemulsion plus an equilibrium lower phase of water depending on the overall composition of the mixture. Such mixtures are defined by the those skilled in the art of surfactant flooding as existing in a Type II(+) phase environment.
A middle-phase microemulsion is a microemulsion in which there is apparently no identifiable external or continuous phase. The structure of the middle-phase microemulsion is still unresolved. A surfactant-oil-water mixture which forms a middle phase microemulsion can equilibrate as a single phase, as two phases of a middle-phase microemulsion plus an equilibrium phase of oil or water, or as three phases. The three phases would be a middle-phase microemulsion plus an equilibrium water phase and an equilibrium oil phase. The end result of the equilibrated microemulsion depends on the overall composition of the mixture. Such mixtures are defined by those skilled in the art of surfactant flooding as existing in Type III phase environments or regimes.
A macroemulsion is a thermodynamically unstable, opaque dispersion of two or more insoluble liquids, one in the other. It is characterized by its propensity to separate into two or more original liquid phases upon standing. The droplet diameters of the dispersed phase range from roughly 200 nanometers to visually resolvable, discreet aggregates. Because of the propensity of a macroemulsion to separate into its components, macroemulsions are not desirable surfactant systems for enhanced oil recovery.
Microemulsions may be used for different chemical purposes. One well known use for oil-in-water microemulsions is to recover oil from underground formations by using the microemulsion in the same fashion as a surfactant slug. But because of the complex phase chemistry involved in microemulsions, the components and concentrations of successful enhanced oil recovery surfactant systems do not necessarily make successful microemulsions, or vice versa. U.S. Pat. Nos. 3,506,070; 3,778,381; 3,981,361; 4,146,499; 4,271,907; 4,318,816; 4,472,291 and 4,946,606 describe the use of various oil-in-water microemulsions for oil recovery.
Oil-in-water microemulsions generally perform better when they are formulated with high equivalent alkane carbon number (EACN) oils having an EACN 50% to 300% higher than the EACN of the crude oil for which the microemulsion is optimized. U.S. Pat. No. 4,318,816 demonstrates that the stability of a single component surfactant such as an alkylarylpolyalkoxyalkylene sulfonate is enhanced when a high EACN oil is added to an aqueous surfactant to form an oil-in-water microemulsion. The high EACN oil raises the phase inversion temperature of the ethoxylated surfactant. U.S. Pat. No. 4,271,907 teaches that water soluble polymers are compatibly incorporated into an optimized microemulsion only when the microemulsion is formulated with a high EACN oil.
U.S. Pat. Nos. 4,756,370, 4,821,803 and 4,822,501 disclose the use of lignin amine surfactant systems wherein a surfactant slug contains water soluble lignin, amine and anionic surfactant. U.S. Pat. No. 4,548,721 claims the use of a surfactant slug to recover oil containing the reaction product of an amine and a lignin.